Rainbow Electronics DS1804 - Manual (Page 2)

DS1804
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OPERATION
The DS1804 is a single nonvolatile potentiometer. The device has a total of 100 tap-points including the
L- and H- terminals. A total of 99 resistive segments exist between the L- and H- terminals. These tap-
points are accessible to the W-terminal, whose position is controlled via a 3-terminal control port. A
block diagram of the DS1804 is shown in Figure 1.
The 3-terminal port of the DS1804 provides an increment/decrement interface which is activated via a
chip select input. This interface consists of the input signals
CS , INC , and U/ D . These input signals
control a 7-bit up/down counter. The output of the 7-bit up/down counter controls a 1 of 100 decoder to
select wiper position. Additionally, this interface provides for a wiper storage operation using the
CS and
INC input control pins. The timing diagram for the 3-terminal interface control is shown in Figure 2.
PIN DESCRIPTIONS
V
CC
- Power Supply. The DS1804 will support supply voltages ranging from +2.7 to +5.5 volts.
GND - Ground.
H - High-Terminal Potentiometer. This is the high terminal of the potentiometer. It is not required that
this terminal be connected to a potential greater than the L-terminal. Voltage applied to the H-terminal
can not exceed the power-supply voltage, V
CC
, or go below ground.
L - Low-Terminal Potentiometer. This is the low terminal of the potentiometer. It is not required that this
terminal be connected to a potential less than the H-terminal. Voltage applied to the L-terminal cannot
exceed the power-supply voltage, V
CC
, or go below ground.
W - Wiper of the Potentiometer. This pin is the wiper of the potentiometer. Its position on the resistor
array is controlled by the 3-terminal control port. Voltage applied to the wiper cannot exceed the power-
supply voltage, V
CC
, or go below ground.
CS - Chip Select. The CS input is used to activate the control port of the DS1804. This input is active
low. When in a high-state, activity on the INC and U/ D port pins will not affect or change wiper
position.
INC - Wiper Movement Control. This input provides for wiper position changes when the CS pin is low.
Wiper position changes of the W-terminal will occur one position per high-to-low transition of this input
signal. Position changes will not occur if the
CS pin is in a high state.
U/ D - Up/Down Control. This input sets the direction of wiper movement. When in a high state and CS
is low, any high-to-low transition on INC will cause a one position movement of the wiper towards the
H-terminal. When in a low state and CS is low, any high-to-low transitions on INC will cause the
position of the wiper to move towards the L-terminal.